This invention relates to an adjustable viewing frame of a type used by artists and others to help to compose a view. One known such frame comprises no more than a piece of card with a square or rectangle cut out of it. Another known such frame comprises a piece of glass or transparent plastic with a square or rectangle marked on it. Such frames are light and easy to make, but they are not readily adjustable to form apertures of different sizes or proportions.
Adjustable frames are known for cropping pictures or photographs. These are usually made from two L-shape pieces of cardboard, plastic, metal or the like which are either separate or mounted to be carried on a board. It is not easy to hold up two separate pieces in just one hand for framing a field of view, which would be useful for an artist, especially in the absence of any means for holding their two pieces in a fixed position relative to one another. The picture-cropping frame cannot be used for this purpose, however because of its weight, which inhibits the user from carrying them, and, especially from holding them up in one hand while drawing or painting with the other.
The prior art also includes the frame described in U.S. Pat. No. 1,183,977 which comprises four rectilinear arms with elongate central slots in them. The arms are held together in pairs by respective nuts and bolts, and the two structures thus formed are held together but threaded pins passing through the slots onto which are screwed thumb nuts to clamp a so-called spider into the slots. This device has the advantage that it can be folded into a compact space, but the disadvantage that it is complex, involving many parts, and requires that the two thumb nuts be slackened to allow adjustment and then re-tightened when the adjustment is made. It is also difficult to set this up with the corners exactly square.
One aspect of the present invention is to provide an adjustable viewing frame which is an improvement over the prior art.
Another aspect of the invention is to provide a viewing frame, which is quick and simple to adjust, light in weight and economical to produce.
Still another aspect of the invention is to provide a viewing frame which can be easily adjusted to a predetermined ratio of side sizes to form a viewing aperture of selected shape.
A further aspect of the invention is a viewing frame which can be held in one hand for use or easily mounted on an easel or other support for use by an artist.
The present invention provides an adjustable viewing frame comprising at least two frame members having arms forming substantially rectilinear frame limbs, in which the frame members are held together by a frictional force which is sufficient to retain the frame members in a selected adjusted position but which can be overcome to effect adjustment. The frictional force can be applied by retainer members. Such retainer members may be resiliently biased into engagement with the said frame members.
In one embodiment the retainer members are generally C-shape and engage respective frame members from opposite sides thereof.
Each limb of a frame member preferably has a respective shoulder extending at least along a part of the length thereof. Such shoulder is engageable by the retainer members in order to hold the frame members together.
The said shoulders of the frame limbs may comprise the side wall of an upstanding ridge or rib extending longitudinally at least part of the way along the frame limb. If the frame limbs are laminar or sheet like elements the longitudinal ridge or ribs may be located substantially along one edge thereof. Alternatively, the said shoulder may be formed by an elongate, longitudinally extending, slot, groove or channel in each frame limb. In such case the retainer members may have heads engaged in the said slot, groove or channel of respective frame limbs whereby to hold them together to form the said frame.
The frictional engagement of the two frame members is preferably achieved by resilient deformation of the retainer members. Such resilient deformation may be flexure, extension or compression.
The present invention also comprehends an adjustable viewing frame comprising at least two frame members having arms forming substantially rectilinear frame limbs, in which the frame members are held together by magnetic attraction sufficient to generate a frictional force which retains the frame members in a selected adjusted position, but which can be overcome to effect adjustment.
For this purpose at least part of at least one of the said frame members may be magnetised and at least part of the other frame member may be made of ferromagnetic material. The magnetic attraction may be effected, of course, by the introduction of appropriate magnetic materials into otherwise non-magnetic members or elements such as plastics. Alternatively, plastics or other non-magnetic materials having magnetic or magnetised particles imbedded therein may be employed.
The adjustable frame of the invention may further include mounting means for mounting the frame to an easel, stand, tripod, table or other support. Such mounting means may also be used as a hand grip by which the frame may be held for viewing.
According to another aspect the present invention provides an adjustable viewing frame comprising two generally L-shape frame members, each having two substantially orthogonal rectilinear frame limbs, and means for retaining the two members together in a selected relative position to form a relatively rectangular frame, in which the frame limbs of at least one frame member bear a scale including indicia representing different dimensional ratios to which the viewing frame may be adjusted.
The invention will be more easily understood from the following detailed descriptions thereof with reference to the drawings.